Eli5 Why there are so many rivets on fighter jets and why not use welding instead?
In: 3
Simple answer, they are not.
Modern 4/5th generation jets are composite built without rivets or welding, instead using composite binding, glues or printed parts.
Fighters you see with rivets which many are still operating such as Mig 23 or mirage 3 were developed in the 1960s, when riveting was still optimal for aircraft as the alternative was screws. However, even then, they weren’t used uniformly. Solid rivets, semi tubular, blind and Huk rivets were all used. The choice was dictated by the requirements of the area of the plane, such as weight, tensile strength, sheer strength.
Simple answer, they are not.
Modern 4/5th generation jets are composite built without rivets or welding, instead using composite binding, glues or printed parts.
Fighters you see with rivets which many are still operating such as Mig 23 or mirage 3 were developed in the 1960s, when riveting was still optimal for aircraft as the alternative was screws. However, even then, they weren’t used uniformly. Solid rivets, semi tubular, blind and Huk rivets were all used. The choice was dictated by the requirements of the area of the plane, such as weight, tensile strength, sheer strength.
Many reasons:
First, Aircraft frame’s metal aren’t exactly sturdy, making the strength provided by weld kind of useless, Aluminum welding, when done right, is very tricky, its not like working with iron or steel.
Second, unlike road vehicles, aircraft are prone to damage, a single debris hit can tear out massive metal skin patches. having rivets lets you replace those patches with “relative” ease.
Third, rivet are MUCH easier to inspect than welding, especially for fighter jets where you need to turn over and rearm in very short time.
Also, rivet can withstand vibration better.
Then theres the cost and maintainer aspect, not only do you need to keep a welding tool but also train the techs to be proficient in wielding, where as rivet is… pretty straight forward.
Many reasons:
First, Aircraft frame’s metal aren’t exactly sturdy, making the strength provided by weld kind of useless, Aluminum welding, when done right, is very tricky, its not like working with iron or steel.
Second, unlike road vehicles, aircraft are prone to damage, a single debris hit can tear out massive metal skin patches. having rivets lets you replace those patches with “relative” ease.
Third, rivet are MUCH easier to inspect than welding, especially for fighter jets where you need to turn over and rearm in very short time.
Also, rivet can withstand vibration better.
Then theres the cost and maintainer aspect, not only do you need to keep a welding tool but also train the techs to be proficient in wielding, where as rivet is… pretty straight forward.
Many reasons:
First, Aircraft frame’s metal aren’t exactly sturdy, making the strength provided by weld kind of useless, Aluminum welding, when done right, is very tricky, its not like working with iron or steel.
Second, unlike road vehicles, aircraft are prone to damage, a single debris hit can tear out massive metal skin patches. having rivets lets you replace those patches with “relative” ease.
Third, rivet are MUCH easier to inspect than welding, especially for fighter jets where you need to turn over and rearm in very short time.
Also, rivet can withstand vibration better.
Then theres the cost and maintainer aspect, not only do you need to keep a welding tool but also train the techs to be proficient in wielding, where as rivet is… pretty straight forward.
For complex reasons, welds on aluminum are not as strong as the base metal. With steel the opposite is usually the case. Welds on high strength aluminum grades (which have been carefully heat treated to maximize strength) may suffer from a 30%-60% loss of strength in the heat-affected zone around the welds.
This effect can be remedied in some cases by heat treating a welded assembly a second time, but that tends to cause thermal distortion. It wouldn’t be practical to heat treat an entire assembled airframe. The typical proceedure is to heat the aluminum to about 50- 100 degrees below it’s melting point, then rapid cool by quenching in water or with a water spray. Then aging- tempering at about modest temperatures of about 220° C. At such high temperatures aluminum becomes quite soft and the entire airframe might sag and buckle like wet cardboard.
Very high strength, high performance aluminum alloys used in aerospace tend to have very poor weldability, and almost invariably have tiny weld cracks that are hard to detect.
Rivets are reliable. Quality of installation doesn’t tend to have a major effect on joint strength, as long as the holes are drilled and countersunk with appropriate tools.
Rivets are fairly easy to inspect.
A rivet failure or two in most case won’t result in catastrophic joint failure. Cracks in a single rivet have a hard time propagating to nearby rivets. Very small cracks in aluminum welds could easily grow larger due to heavy vibration.
For complex reasons, welds on aluminum are not as strong as the base metal. With steel the opposite is usually the case. Welds on high strength aluminum grades (which have been carefully heat treated to maximize strength) may suffer from a 30%-60% loss of strength in the heat-affected zone around the welds.
This effect can be remedied in some cases by heat treating a welded assembly a second time, but that tends to cause thermal distortion. It wouldn’t be practical to heat treat an entire assembled airframe. The typical proceedure is to heat the aluminum to about 50- 100 degrees below it’s melting point, then rapid cool by quenching in water or with a water spray. Then aging- tempering at about modest temperatures of about 220° C. At such high temperatures aluminum becomes quite soft and the entire airframe might sag and buckle like wet cardboard.
Very high strength, high performance aluminum alloys used in aerospace tend to have very poor weldability, and almost invariably have tiny weld cracks that are hard to detect.
Rivets are reliable. Quality of installation doesn’t tend to have a major effect on joint strength, as long as the holes are drilled and countersunk with appropriate tools.
Rivets are fairly easy to inspect.
A rivet failure or two in most case won’t result in catastrophic joint failure. Cracks in a single rivet have a hard time propagating to nearby rivets. Very small cracks in aluminum welds could easily grow larger due to heavy vibration.
For complex reasons, welds on aluminum are not as strong as the base metal. With steel the opposite is usually the case. Welds on high strength aluminum grades (which have been carefully heat treated to maximize strength) may suffer from a 30%-60% loss of strength in the heat-affected zone around the welds.
This effect can be remedied in some cases by heat treating a welded assembly a second time, but that tends to cause thermal distortion. It wouldn’t be practical to heat treat an entire assembled airframe. The typical proceedure is to heat the aluminum to about 50- 100 degrees below it’s melting point, then rapid cool by quenching in water or with a water spray. Then aging- tempering at about modest temperatures of about 220° C. At such high temperatures aluminum becomes quite soft and the entire airframe might sag and buckle like wet cardboard.
Very high strength, high performance aluminum alloys used in aerospace tend to have very poor weldability, and almost invariably have tiny weld cracks that are hard to detect.
Rivets are reliable. Quality of installation doesn’t tend to have a major effect on joint strength, as long as the holes are drilled and countersunk with appropriate tools.
Rivets are fairly easy to inspect.
A rivet failure or two in most case won’t result in catastrophic joint failure. Cracks in a single rivet have a hard time propagating to nearby rivets. Very small cracks in aluminum welds could easily grow larger due to heavy vibration.
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